The invention relates to a screwing element for holding and for forcibly turning a fastener, with a plurality of jaws, which are disposed in succession in circumferential direction for seizing the fastener, wherein the jaws engage in a tubular holder and, in cooperation with this holder, in a first end position can be forced radially apart for the purpose of holding the fastener, and in a second end position can be radially squeezed toward each other by mechanical action of the holder in response to application of axial and/or radial force.
Such screwing elements have become known in a plurality of different embodiments. As a rule, such screwing elements have a recess for accommodating the fastener head, wherein the recess as viewed in axial direction has a cross section matched to the cross section of the fastener head, so that torque can be transmitted while the fastener is being driven in. Accordingly a fastener is guided axially with its head in the recess in such a screwing element. Spring-loaded pins or balls can also be disposed, for example, to prevent the head of a fastener from slipping out spontaneously after it has been inserted in the screwing element. Thus captive protection is achieved at least temporarily. If such a fastener is to be driven into a corresponding workpiece, however, then axial force transmission is also needed, and so appropriate stop elements must in turn be provided in a screwing element in order to limit movement toward the screwing element. Since the diameter of the threaded shank of the fastener is normally much smaller than the diameter of the fastener head, it is usually even necessary to provide centering for the shank, in order that proper setting of the fastener can be achieved at all.
The object of the present invention is therefore to provide a screwing element of the type mentioned in the introduction; with which element a fastener head or portions of a fastener head can be immobilized in axial direction during setting of a fastener, specifically until the fastener is finally tightened.
This object is achieved according to the invention by the fact that incisions or recesses are formed on the free end region of the jaws for mechanical and/or frictional accommodation of a fastener head, and that gripper-like parts jutting outwardly toward the central axis or directed away therefrom are formed on the free end of the jaws, adjoining the incisions or recesses, for the purpose of additional mechanical and/or frictional seizing of portions of the fastener head.
By means of the screwing element according to the invention, the fasteners to be inserted can be clamped in the region of the fastener head in such a way that they can no longer be moved in axial direction, and that they remain axially aligned with the screwing element throughout the entire setting process and thus permit optimal drive action by a driving tool. Because of the radial squeezing effect of corresponding jaws, not only can the fastener head be seized exactly, but also corresponding engagement with the fastener head from behind is possible without the need for additional stop elements and studs or balls which spring back under spring loading.
To achieve particularly good alignment between screwing element and fastener and to permit exact clamping of the fastener head, it is provided that the incisions, recesses or the like on the jaws correspond at least approximately to the cross section of the rim region of the fastener head to be seized or of a shoulder formed thereon. The screwing element or the jaws thereof can be adapted to a specially formed fastener, to the effect that a highly special screwing element, with which the fasteners can also be optimally set, is available for a given individual application.
In order to achieve proper torque transfer during a boring process, a thread-forming process or merely during the process of driving in a fastener, it is proposed that, in the region of the incisions, recesses or the like or adjoining these at offset position in axial direction or even on the gripper-like parts or openings or profiled structures, there be provided extensions of a tool for acting on a fastener head or on portions thereof. In this way optimal torque transfer is achieved in addition to the mechanical holding effects of the jaws, by the fact that extensions of a tool are provided precisely in the affected regions of the jaws.
In this connection it is advantageous for the jaws to be spring-loaded toward their open position. Thus, when the jaws are in open position, they are always pivoted away from each other, and so no problems of any kind occur for insertion of the next fastener.
To ensure that the jaws do not come into contact with the surface of the workpiece until a fastener has just been finally set, it is provided that the thickness of the gripper-like portions viewed in axial direction of the screwing element is smaller than the axial length of a fastener-head portion which on the shank side adjoins a shoulder formed circumferentially on the fastener head. In all cases, therefore, the lowest edge of the jaws and thus of the gripper-like parts is still disposed at a corresponding distance from the surface of the workpiece, and so the fastener head can be immobilized until setting has just been completed, without scratching of the workpiece-surface.
A simple structural variant provides that, on the inside of the holder and/or on the outside surface of the jaws, there are formed camming surfaces which taper sharply relative to the central axis, wherein the jaws can be squeezed toward each other by the camming surfaces in response to being forced axially into the holder. In this way forced closing of the jaws can be achieved with simple means, specifically merely by pushing the fastener axially inward, wherein the fastener head acts appropriately on the jaws. If axial pressure is additionally exerted by the driving tool during the setting process, the sharply tapering camming surfaces generate an additional radial component of force, thus clamping the fastener head even more forcefully during the process of setting of the fastener.
To ensure that satisfactory force transmission can occur, it is advantageous for sharply tapering camming surfaces to be provided on both the holder and on the jaws.
In a particular structural variant, it is further provided that the jaws are equipped at their ends protruding into the tubular holder with radially inwardly directed toes, which engage in a radially circumferential groove of a stud that is axially slidable in the screwing element and can be fixed in a plurality of latching positions, wherein this stud can be positioned together with the jaws by the action of axial pushing or pulling thereon.
In this way the jaws are secured not only in axial direction and thus held captively, but thereby can also be brought into a specific open end position and closed end position in cooperation with the stud. Since the jaws in one of their end positions remain in the closed position, the fastener head cannot fall out downward again, even during assembly, after insertion between the jaws. In this precise connection it is advantageous for the stud to be fixed latchingly at least in the two end positions of the jaws.
For this purpose it is proposed that the stud be provided with at least two latching positions formed by circumferential grooves, wherein a spring-loaded pin or a ball which engages in the corresponding circumferential groove is held against the tubular holder. Thereby there are created secure latching positions, which prevent inadvertent maladjustment of the jaws in the open position and in the closed position.
To achieve optimal cooperation between the stud and the jaws cooperating mechanically or frictionally with the stud, it is proposed that the stud, on its portion adjoining the groove for engagement with the toes formed on the jaws, be adapted to the inside cross section of the jaws in closed condition, wherein the transition between the groove and the end part of the stud and the corresponding regions of the jaws are spherically convex. This ensures not only exact guidance between the stud and the jaws, but also exact pivoting capability without tilting and thus without operating disturbances for the screwing element.
Further technical possibilities are achieved by the construction of a screwing element according to the invention. In one particular embodiment, for example, a tool for an internal drive can be formed at the center between the jaws. In such a case the jaws are needed practically only for immobilizing and axially aligning the fastener, whereas the motive power for driving in can be provided via an internal drive. In such a construction it is particularly advantageous for the tool for an internal drive to be formed or disposed at the free end of the stud which is slidable in the tubular holder. This stud slides together with the jaws and always occupies the same axial position relative to the jaws, so that it is very simple to equip the free end of this stud with the appropriate internal drive. Since the fastener head is axially immobilized, the internal drive also cannot be forced out of the corresponding recess of the fastener head. Thereby a relatively high torque can be transmitted, even when the length of axial engagement offered by the internal drive is relatively small.
In an advantageous alternative embodiment, it is proposed that the jaws be squeezed resiliently toward each other by an O-ring inlaid in a groove on the outside circumference of the jaws in the region of the inwardly projecting toes, so that the jaws are pressed apart into open position when in their position withdrawn from the holder. Thus there is created a structurally very simple variant, which on the one hand generates the resilient effect and on the other hand creates corresponding retention of the jaws relative to the stud.
Another embodiment provides that compression springs are inserted between the jaws in the region of their free ends, so that the jaws, when in their position withdrawn from the holder, are forced apart into open position. By these features there is achieved practically the same effect, since the intended purpose in both embodiments is that the ends of the jaws protruding into the holder or the toes thereof remain constantly pressed against the stud.
To achieve optimal retention of an inserted fastener head, it is proposed that the gripper-like parts each be extended over the entire sector region of the jaws. In this way the best possible all-around retention over the circumference of the fastener head is assured. An optimal and very simple construction is further achieved by providing two jaws extending approximately over an angular region of 180xc2x0.